Filter cleaning method

Abstract

Provided is a filter cleaning method capable of efficiently reducing particles generated from unused filters. The filter cleaning method comprises: a first cleaning step of cleaning a fluoropolymer filter with ozone water as a first cleaning liquid; and a second cleaning step of cleaning the filter after the first cleaning step with an acid-containing liquid or an alkali-containing liquid as a second cleaning liquid.

Description

Filter cleaning method

[0001] The present invention relates to a filter cleaning method.

[0002] BACKGROUND ART A filter used in a silicon wafer cleaning process for cleaning silicon wafers is known (see, for example, Patent Document 1).

[0003] JP 2015-139734 A

[0004] When an unused filter is used for cleaning silicon wafers, it is preferable to reduce particles such as metals generated from the filter in advance.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a filter cleaning method that can efficiently reduce particles generated from unused filters.

[0006] One aspect of the present invention is as follows.

[0007] [1] A filter cleaning method comprising: a first cleaning step of cleaning a fluororesin filter with ozone water as a first cleaning liquid; and a second cleaning step of cleaning the filter after the first cleaning step with an acid-containing liquid or an alkali-containing liquid as a second cleaning liquid.

[0008] [2] The filter cleaning method according to [1], wherein the ozone concentration of the first cleaning liquid in the first cleaning step is 5 ppm or more and 40 ppm or less, and the flow rate of the first cleaning liquid in the first cleaning step is 2 L / min or more and 20 L / min or less.

[0009] [3] The filter cleaning method according to [1] or [2], wherein the first cleaning liquid is passed through the filter for one hour or more in the first cleaning step.

[0010] [4] The filter cleaning method according to any one of [1] to [3], wherein the second cleaning liquid is hydrofluoric acid or an aqueous solution containing ammonia and hydrogen peroxide.

[0011] [5] The filter cleaning method according to any one of [1] to [4], wherein the second cleaning step includes a second cleaning liquid circulation step of passing the second cleaning liquid through the filter and circulating the second cleaning liquid after passing through the filter.

[0012] [6] The filter cleaning method according to [5], wherein the second cleaning step includes a pure water supply step of replacing the second cleaning liquid with pure water and passing the pure water through the filter, a particle measurement step of measuring the number of particles in the pure water after the pure water supply step, and a calculation step of calculating an attenuation amount of the particle number from the measurement result of the particle measurement step, and the second cleaning liquid circulating step, pure water supply step, particle measurement step, and calculation step are repeated in this order until the attenuation amount reaches a predetermined standard.

[0013] [7] The filter cleaning method according to any one of [1] to [6], wherein the filter is a PTFE membrane.

[0014] [8] A silicon wafer cleaning method, comprising: a filter cleaning step of cleaning the filter by the filter cleaning method according to any one of [1] to [7]; and cleaning silicon wafers using the filter that has been cleaned by the filter cleaning step.

[0015] [9] The silicon wafer cleaning method according to [8], wherein a silicon wafer cleaning step of cleaning a silicon wafer using the filter cleaned in the filter cleaning step includes a third cleaning liquid circulating step of passing a third cleaning liquid through the filter and circulating the third cleaning liquid after passing through the filter, and wherein the second cleaning liquid passed through the filter in the second cleaning step of the filter cleaning step has the same components as the third cleaning liquid.

[0016]

[10] The silicon wafer cleaning method according to [9], wherein a concentration of the component other than water in the second cleaning liquid passed through the filter in the second cleaning step of the filter cleaning step is greater than a concentration of the component in the third cleaning liquid, and when the second cleaning liquid contains a plurality of components other than water, the concentration of each of the components other than water in the second cleaning liquid is greater than the concentration of the component in the third cleaning liquid.

[0017]

[11] The silicon wafer cleaning method according to

[10] , wherein the concentration of the component other than water in the second cleaning liquid passed through the filter in the second cleaning step of the filter cleaning step is more than 1 time and not more than 5 times the concentration of the component in the third cleaning liquid, and when the second cleaning liquid contains a plurality of components other than water, the concentration of each of the components other than water in the second cleaning liquid is more than 1 time and not more than 5 times the concentration of the component in the third cleaning liquid.

[0018] According to the present invention, it is possible to provide a filter cleaning method that can efficiently reduce particles generated from an unused filter.

[0019] FIG. 1 is a flow diagram showing a silicon wafer cleaning method according to an embodiment of the present invention.

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] As shown in FIG. 1 , in one embodiment of the present invention, the filter cleaning method includes a first cleaning step S11 in which a fluororesin filter is cleaned with ozone water as a first cleaning liquid, and a second cleaning step S12 in which the filter after the first cleaning step S11 is cleaned with an acid-containing liquid or an alkali-containing liquid as a second cleaning liquid.

[0022] According to the above configuration, particles such as metal particles adhering to an unused filter are easily peeled off from the filter by the oxidizing action of ozone water as the first cleaning liquid, and the particles can be easily removed by the acid-containing or alkali-containing liquid as the second cleaning liquid, thereby efficiently reducing particles from the filter. Thus, a filter cleaning method that can efficiently reduce particles generated from an unused filter can be realized.

[0023] The ozone concentration of the first cleaning solution in the first cleaning step S11 is 5 ppm or more and 40 ppm or less, and the flow rate of the first cleaning solution in the first cleaning step S11 is 2 L / min or more and 20 L / min or less. According to the above configuration, the first cleaning solution can more easily remove particles from the filter, making it easier to efficiently reduce particles generated from unused filters. If the ozone concentration of the first cleaning solution is less than 5 ppm, it is difficult to achieve a particle reduction effect, and if it exceeds 40 ppm, it is likely to damage the filter and reduce its filter function.

[0024] In the filter cleaning method, a first cleaning liquid is passed through the filter for at least one hour in the first cleaning step S11. According to the above configuration, the first cleaning liquid can further facilitate the removal of particles from the filter, thereby making it easier to efficiently reduce particles generated from an unused filter.

[0025] The second cleaning liquid is hydrofluoric acid or an aqueous solution containing ammonia and hydrogen peroxide. According to the above configuration, the second cleaning liquid can further facilitate removal of particles, making it easier to efficiently reduce particles generated from unused filters.

[0026] The second cleaning step S12 includes a second cleaning liquid circulation step S121 in which the second cleaning liquid is passed through a filter and the second cleaning liquid is circulated through the filter. According to the above configuration, particles can be removed from the filter while circulating the second cleaning liquid in the second cleaning liquid circulation step S121, thereby reducing the amount of expensive second cleaning liquid used. Therefore, it is easy to economically reduce particles generated from unused filters.

[0027] The second cleaning step S12 includes a pure water supply step S122 in which the second cleaning liquid is replaced with pure water and the pure water is passed through a filter, a particle measurement step S123 in which the number of particles in the pure water after the pure water supply step S122 is measured, and a calculation step S124 in which the attenuation of the particle number is calculated from the measurement result of the particle measurement step S123. The second cleaning liquid circulation step S121, the pure water supply step S122, the particle measurement step S123, and the calculation step S124 are repeated in this order until the attenuation reaches a predetermined standard. According to the above configuration, by appropriately setting the predetermined standard, it is possible to reduce particles generated from an unused filter to a desired level.

[0028] The filter is a PTFE membrane. PTFE membranes have excellent chemical resistance, heat resistance, and weather resistance. Because PTFE membranes have a porous structure and are hydrophobic, it is desirable to use a PTFE membrane that has been hydrophilized to improve permeability. For example, known methods can be used for hydrophilization, such as passing a solvent such as IPA through the PTFE membrane and then flushing it with pure water.

[0029] In this embodiment, the silicon wafer cleaning method includes a filter cleaning step S1 in which a filter is cleaned by a filter cleaning method, and the silicon wafer is cleaned using the filter that has been cleaned in the filter cleaning step S1. According to the above configuration, it is possible to realize a silicon wafer cleaning method that can efficiently reduce particles generated from an unused filter prior to cleaning of the silicon wafer.

[0030] The silicon wafer cleaning process S2, which cleans silicon wafers using a filter cleaned in the filter cleaning process S1, includes a third cleaning liquid circulation process S21, which passes a third cleaning liquid through the filter and circulates the third cleaning liquid after passing through the filter, and the second cleaning liquid passed through the filter in the second cleaning process S12 of the filter cleaning process S1 has the same components as the third cleaning liquid. According to the above configuration, since the silicon wafers can be cleaned while circulating the third cleaning liquid in the third cleaning liquid circulation process S21, the amount of expensive third cleaning liquid used can be reduced, and silicon wafers can be cleaned economically. Furthermore, by using a filter cleaned with a second cleaning liquid having the same components as the third cleaning liquid, silicon wafers can be cleaned efficiently.

[0031] The second cleaning liquid passed through the filter in the second cleaning step S12 of the filter cleaning step S1 has a higher concentration of components other than water than the third cleaning liquid, and if the second cleaning liquid contains multiple components other than water, the concentration of each of the components other than water in the second cleaning liquid is higher than the concentration of the corresponding component in the third cleaning liquid. According to the above configuration, the filter can be efficiently cleaned using the second cleaning liquid, which has a higher concentration than the third cleaning liquid.

[0032] The concentration of the components other than water in the second cleaning liquid passed through the filter in the second cleaning step S12 of the filter cleaning step S1 is more than 1 to 5 times the concentration of the corresponding component in the third cleaning liquid, and if the second cleaning liquid contains multiple components other than water, the concentration of each component other than water in the second cleaning liquid is more than 1 to 5 times the concentration of the corresponding component in the third cleaning liquid. This configuration makes it easier to efficiently clean the filter with the second cleaning liquid of an appropriate concentration.

[0033] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be modified in various ways without departing from the gist of the present invention.

[0034] The number of particles in the liquid of 20 nm or larger during the acid treatment was measured using a liquid particle counter in two cases: one in which ozone water was passed through the filter (10 ppm, 10 L / min, 6 hours) and then an acid-containing liquid was passed, and one in which pure water was passed through the filter without ozone water at the same flow rate as the ozone water treatment for the same time (10 L / min, 6 hours) and then an acid-containing liquid was passed. The measurement results are shown in Table 1. It can be seen that performing ozone water treatment can promote a reduction in the amount of particles generated from the filter.

[0035] S1 Filter cleaning step S11 First cleaning step S12 Second cleaning step S121 Second cleaning liquid circulation step S122 Pure water supply step S123 Particle measurement step S124 Calculation step S2 Silicon wafer cleaning step S21 Third cleaning liquid circulation step

Claims

1. A filter cleaning method comprising: a first cleaning step of cleaning a fluororesin filter with ozone water as a first cleaning liquid; and a second cleaning step of cleaning the filter after the first cleaning step with an acid-containing liquid or an alkali-containing liquid as a second cleaning liquid.

2. A filter cleaning method as described in claim 1, wherein the ozone concentration of the first cleaning liquid in the first cleaning process is 5 ppm or more and 40 ppm or less, and the flow rate of the first cleaning liquid in the first cleaning process is 2 L / min or more and 20 L / min or less.

3. A filter cleaning method according to claim 1, wherein in the first cleaning step, the first cleaning solution is passed through the filter for one hour or more.

4. The filter cleaning method according to claim 1, wherein the second cleaning liquid is hydrofluoric acid or an aqueous solution containing ammonia and hydrogen peroxide.

5. A filter cleaning method as described in claim 1, wherein the second cleaning process includes a second cleaning liquid circulation process for passing the second cleaning liquid through the filter and circulating the second cleaning liquid after passing through the filter.

6. A filter cleaning method as described in claim 5, wherein the second cleaning step includes a pure water supply step of replacing the second cleaning liquid with pure water and passing the pure water through the filter, a particle measurement step of measuring the number of particles in the pure water after the pure water supply step, and a calculation step of calculating an amount of attenuation of the number of particles from the measurement results in the particle measurement step, and the second cleaning liquid circulating step, pure water supply step, particle measurement step and calculation step are repeated in this order until the amount of attenuation reaches a predetermined standard.

7. The filter cleaning method of claim 1, wherein the filter is a PTFE membrane.

8. A silicon wafer cleaning method, comprising a filter cleaning step of cleaning the filter by the filter cleaning method according to any one of claims 1 to 7, and cleaning silicon wafers using the filter that has been cleaned by the filter cleaning step.

9. A silicon wafer cleaning method according to claim 8, wherein a silicon wafer cleaning step of cleaning silicon wafers using the filter cleaned in the filter cleaning step includes a third cleaning liquid circulating step of passing a third cleaning liquid through the filter and circulating the third cleaning liquid after passing through the filter, and wherein the second cleaning liquid passed through the filter in the second cleaning step of the filter cleaning step is composed of the same components as the third cleaning liquid.

10. A silicon wafer cleaning method according to claim 9, wherein a concentration of the component other than water in the second cleaning liquid passed through the filter in the second cleaning step of the filter cleaning process is greater than a concentration of the corresponding component in the third cleaning liquid, and when the second cleaning liquid contains a plurality of components other than water, the concentration of each of the components other than water in the second cleaning liquid is greater than the concentration of the corresponding component in the third cleaning liquid.

11. A silicon wafer cleaning method according to claim 10, wherein the concentration of the component other than water in the second cleaning solution passed through the filter in the second cleaning step of the filter cleaning process is more than 1 time and not more than 5 times the concentration of the component in the third cleaning solution, and when the second cleaning solution contains a plurality of components other than water, the concentration of each of the components other than water in the second cleaning solution is more than 1 time and not more than 5 times the concentration of the component in the third cleaning solution.

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